Introduced September 2023.
The updates on this PCB are
a) mistakes & omissions corrected
b) The bias spreader is now a complementary pair which is less prone to supply line fluctuations. The temperature coefficient of the bias voltage is now variable according to component values in the bias chain.
c) The protection mechanism uses a npn/pnp pair as a thyristor latch. This could false trigger when hot and initiate a shutdown. The PNP device now has a turn off resistor to prevent this.
This is the higher power version of the PCB. The lower power version has 2 power transistors instead of 4.